## Topology & Geometric Group Theory Seminar

## Spring 2009

### 1:30 – 2:30, Malott 207

Tuesday, February 17

**Pierre
Py**, University of Chicago

*Quasi-morphisms and area-preserving homeomorphisms*

I will recall the notion of a quasi-morphism on a group and describe a
few examples of quasi-morphisms defined on groups of Hamiltonian
diffeomorphisms of surfaces. Then we will try to answer the following
question: which quasi-morphisms on these groups are continuous for the
C^{0}-topology? This question is related to the problem of
the simplicity of the group of compactly supported area-preserving
homeomorphisms of the disc. This is based on a joint work with
M. Entov and L. Polterovich. This is also related to a
recent work of Le Roux.

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